The voltage-gated sodium channel is the biochemical basis of excitability in many nerve, muscle and secretory cells. Therefore, activation of sodium channel gene expression is a prerequisite for the development of excitability in these cell types. The long-term goal of our research is to elucidate the molecular events involved in tissue-specific and developmental regulation of the mammalian sodium channel genes. We have proposed three specific aims to achieve this goal, which make use of genomic clones specific for the brain type I and type II sodium channels. First, we will identify the DNA elements responsible for tissue-specific expression of the type I and type II genes. For these studies, the putative regulatory regions of the sodium channel genes will be dissected by deletional analysis and fused to a easily assayable reporter gene. Biological activity of the fusion genes will be determined in cell lines and in transgenic mice. Second, we will determine whether there are specific elements in the type I and type II genes that are required for their activation during neuronal differentiation. The expression of sodium channel fusion genes will be studied in the nervous system of developing transgenic mice and in a tissue culture model for neuronal differentiation. Third, we will characterize the cellular factors that regulate sodium channel gene expression in neuronal cells. A novel strategy for directly cloning specific DNA-binding proteins will be tested. These studies will provide a framework for understanding the molecular mechanisms involved in the development of excitability. They will also provide information on the elements in neuronal genes that are responsible for directing expression to specific cell types within the nervous system.